Not Applicable.
This invention relates to a fuel delivery system for two-cycle and four-cycle internal combustion engines, and more particularly, for a feedback fuel regulator for use on model aircraft, comprising a microprocessor, an in-line fuel valve, and one or more engine operating condition sensors including an exhaust gas temperature sensor, to regulate the optimum fuel mixture. While the invention is described in detail with respect to its application in model aircraft engines, those skilled in the art will recognized the wider applications of the inventive principles disclosed hereafter.
A typical model airplane engine 10 (FIGS. 1A-1C) is a single cylinder engine having a very simple carburetor 12 including a fixed bore single air intake venturi and a non-variable fuel jet orifice at a constant throttle valve position, without a fuel bowl for air and fuel intake. The typical engine 10 additionally includes a very simple single-chamber expansion type of muffler 14 connected to the engine exhaust port 16 for handling and muffling exhaust gasses. The air flow through the air intake venturi produces in the venturi throat a partial vacuum which draws fuel into the intake airstream from the engine fuel tank, through the fuel jet. Fuel pressure conventionally is also supplied from the exhaust back pressure, commonly connected to the fuel tank. The carburetor has a throttle valve 18 which is adjustable to regulate air and fuel flow to the engine, and thereby regulate the speed of the engine 10. It is well known in the art that the venturi partial vacuum is rather weak, and results in extremely unreliable engine operation due to variations in aircraft attitude in flight causing variations in fuel head pressure and also due to extremely high centrifugal forces imposed on the aircraft during aerobatics maneuvers, routinely exceeding ten times the gravitational force.
Accordingly, conventional fuel systems fail to produce optimum fuel regulation for maximum power and fuel efficiency. It is known in the art that a doubling in the rate of air intake into a fixed bore single air intake venturi will cause a four-fold increase in venturi partial vacuum fuel draw. This means that at a constant degree of throttle opening in a model aircraft engine, as the engine increases in revolution per minute (rpm) during acceleration, a disproportionately higher amount of fuel than air will be drawn in to the carburetor, causing a rich mixture and inefficient operation. A rich mixture decreases the available torque and limits the engine""s power potential as it gains speed. The most efficient way to extract power from a model aircraft engine is to have the engine run at full throttle, turning a large size propeller 20 of low to medium pitch, at the rpm of maximum torque while standing still (static rpm) to achieve good acceleration to in-flight speeds. The in-flight rpm should correspondingly increase to approach the maximum power peak. However, as the engine unloads in-flight, its fuel-air mixture becomes richer than necessary for producing peak power, hence torque and power decrease despite an increase in engine rpm.
Ideally, to compensate for the increased fuel draw during unloaded in-flight operation, a needle valve 22 in the carburetor 12 is adjusted to decrease the needle-valve opening, and correspondingly the fuel flow, for peak power output every time the engine rpm is allowed to increase by reducing the engine load. However, the carburetor needle valve 22 is normally not manually adjustable in a model aircraft while in flight, and must be set at a fixed setting resulting in less than perfect engine operation prior to each flight.
Among the several objects and advantages of the present invention are:
The provision of a new and improved fuel regulator to optimize the fuel mixture for two-cycle and four-cycle engines;
The provision of the aforementioned fuel regulator which eliminates the need to adjust fuel regulating needle valves;
The provision of the aforementioned fuel regulator which is configured for installation between a fuel tank and a carburetor;
The provision of the aforementioned fuel regulator which includes an exhaust gas temperature sensor to continually regulate fuel mixture;
The provision of the aforementioned fuel regulator which is capable of operation under low fuel pressures, in the range of 1-15 pounds;
The provision of the aforementioned fuel regulator which may include additional inputs from engine operating condition sensors and an exhaust gas temperature sensor to continually optimize the fuel mixture; and
The provision of the aforementioned fuel regulator which is adapted for use in model aircraft engines.
Briefly stated, the fuel regulator of the present invention comprises a microprocessor, a thermal sensing device, which, in the preferred embodiment is a thermocouple operatively arranged to sense exhaust gas temperature, and an in-line fuel regulating valve installed between the fuel tank and the carburetor. During operation, the microprocessor receives signals from the exhaust gas temperature sensor and any additional engine operating condition sensors. These signals are compared with stored reference valve to determine the optimum fuel mixture for the current engine operating conditions. If the current engine operating conditions require a variation in the fuel mixture settings, the microprocessor regulates the degree and/or rate of opening of the in-line fuel regulating value, and accordingly regulates the flow of fuel into the carburetor.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.